ASTRO-PHYSICS 400QMD Quick Start Manual - Page 7

Browse online or download pdf Quick Start Manual for Telescope ASTRO-PHYSICS 400QMD. ASTRO-PHYSICS 400QMD 11 pages. German equatorial mount with dual axis quartz micro-drive

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GUIDE RATES: If you wish to engage the fine guiding rates of 1x, 0.5x, and .25x, move the first switch to GUIDE and

the second switch to the 1x, .5x, or .25x position.

DECLINATION BACKLASH CONTROL: When using the 1x, .5x, and .25x guide rates in declination, you may find

that there is a delay when attempting to reverse the motion of the star. Normally declination drift is only in

one direction, and will require correction with only one button. However, occasionally it may be necessary to

reverse the motion. The multiple gear train inside the drive motors takes a considerable number of pulses to

unwind and rewind in the opposite direction. To compensate for this, we have included a circuit that pulses

the motor very rapidly for a moment before continuing at the slower rate. Because the amount of delay varies

with each motor, we have installed a 10-position switch which can be used to dial in the exact amount of

compensation. Starting from the left, engage one switch at a time into the up position until the delay at .25x

guide rate is minimum. If too many switches are engaged, the star will over shoot the desired position.

PERIODIC ERROR MEMORY (PEM): The drive controller contains a very sophisticated periodic error compensation

circuit. Because the majority of the periodic error is due to the worm and is quite predictable, it is possible to

significantly reduce it by simply having the controller "memorize" your button inputs and automatically play

them back for each cycle of the worm. This circuit has some unique features that makes it easy to operate

and almost totally foolproof.

To start the process of recording the periodic error, align your telescope accurately on the pole so that you get

minimum R.A. and Dec. drift. Place a medium brightness star on the crosshair at moderately high power so

you can easily see the R.A. gear drift. Be sure that the night is steady enough with minimum atmospheric

motion and pick a star near the zenith to minimize atmospheric refraction errors. The recording process will

take about 6.5 minutes to complete.

When you are ready to begin, be sure that the star is on the crosshair, and slide the play/record switch into

the "record" mode. The green LED will come on for the 6-minute period, and will extinguish at the end of the

recording period. During this 6.5-minute period it will be necessary to keep the star on the crosshair. Every

button input will be recorded. Avoid trying to guide out any atmospheric scintillation, since this will add a

random noise error into your final guide rate. If an ST4 autoguider is available, it can be used to guide, and

the controller will faithfully remember each error correction that it makes. An autoguider is extremely

accurate, and will place into the memory a very smooth correction of the gear error.

When you wish to play back the recorded corrections, slide the play/record switch into the "play" mode. The

controller will automatically play back the correct portion of the worm error. It is not necessary to place the

rate switches into the same position that they were recorded in. For the smoothest results, however, it is

advised to record and play back in the .25x position. The controller can be slewed in the 8x and 16x mode at

any time without losing track of the periodic error. The playback can also be turned on and off at any time

without losing track of the gear position.

A most valuable feature of this circuit is that it automatically compensates for any drift inadvertently introduced

by the operator in the process of recording the gear error. For instance, if the mount was not properly polar

aligned in altitude, the right ascension drift rate would be in error. The circuitry automatically subtracts this

slow drift from the memory, so that the overall long-term drive rate remains exactly at the King rate. This way

the compensated driving rate will always be correct for any other position in the sky and for any other time

that the mount is set up in the field. When the mount is properly polar aligned, it is possible to take 15 to 30

minute unguided astrophotos without trailed star images. For more critical exposures, the controller memory

allows the astrophotographer to check the guide star only occasionally during a long exposure.

LED KNOBS: There is an LED output available on the 400 Dec. axis motor housing as shown on Diagram 2. You

may insert your LED reticle to this plug. Brightness can then be controlled using the MIN to MAX (minimum to

maximum) setting of the LED knob.

AUTOGUIDER CONNECTION: If you own a Santa Barbara Instrument Group (SBIG) ST-4 or ST-6 Star

Tracker/Imaging system, connect it to the RJ11 phono plug input of the controller via a TIC (Tracking

Interface Cable) produced by SBIG. You may purchase the cable directly from us (our part #CABTIC) or

directly from SBIG. This cable will have a DB15 female connector on one end and an RJ11 plug on the end

that inserts into our controller.

To operate the SBIG ST-7 or ST-8, you will need the ST-7 cable available from SBIG. This is the same cable

that is offered for the Celestron Ultima. It has a DB9 male connector on one end and an RJ11 connector that

inserts into our controller.